This invention relates to a method of safely and efficiently treating activated carbon which has adsorbed thereon trichloroethylene, tetrachloroethylene, dioxin, PCBs, o-chlorophenol and other organochlorine compounds that are difficult to treat by known chemical or physical means.
There have been available no effective methods for treating organochlorine compounds such as dioxin and PCBs and the only method presently employed is such as to prevent their diffusion by effecting adsorption on activated carbon or some other suitable adsorbent. For example, in order to remove toxic materials such as trichloroetylene that are present in very small amounts in the ppb order in underground water, the water is aerated to enable dissolved trichloroethylene and other toxic materials to be adsorbed on activated carbon.
Conventionally, activated carbon having toxic materials adsorbed thereon is either stored or appropriately treated by incineration or heating in steam. However, the following problems arise with such methods. First, burning in an incinerator involves the possibility that organochlorine compounds adsorbed on activated carbon may be released into the atmosphere. Further, pyrolysis of organochlorine compounds may also result in toxic by-products, such as chlorine gas, phosgene and dioxin being released into the atmosphere in the form of secondary pollution. In addition, the heating of organochlorine compounds with steam yields chlorine gas which is corrosive and the affects walls of a heating furnace (regenerator), in which it is generated, thereby considerably shortening the furnace life.
In both incineration and steam heating, the organic material recombines with chlorine to produce dioxin and other toxic by-products if the treatment temperature is too low. To avoid this problem, it is necessary to reburn the exhaust gas at temperatures higher than 1000.degree. C. which substantially increases the cost of treatment.
Even if organochlorine compounds are exposed to ionizing radiation in a vapor phase, chlorine gas will be produced and may be released into the atmosphere.